Kirkpatrick, who admitted that he hasn't "stopped smiling" since the performance, told radio show Johnny's House that he was anxious about returning to the stage.

"When I was in Miami and we were doing the rehearsals, I was scared to death," he said. "I was like, 'This is for him, I don't want to screw this up for him'. Then we come up here, we see the dancers, I'm like, 'Oh my God, we've got to keep up with this?' I was just so worried about not messing up for him.

"And then yesterday and the day before yesterday, we were all just hanging out, and I was like, 'Man, this is like old times. I could get up there and not know a thing and feel confident with those guys'. And the minute we started coming out, I was like, 'This is a moment I just want to hold on to again'."

Kirkpatrick, who described it as an "honor" to perform with Timberlake again, admitted that he couldn't sleep in the run-up to the reunion and was having "nightmares".

He also admitted that he wasn't expecting the appearance to be so physically demanding, joking that he was coming home from rehearsals "drenched", and revealed that his knee had been a concern.

"I was worried," he joked. "A couple of times it's popped. I'm old, I've got two bad knees now! And dancing on those popups, they had a little give to them and I was a little nervous. I was joking with Justin, because we were doing rehearsals and I went the wrong way a little bit. Back in the day, he's like, 'Are you okay, do you get it?' Now he's like, 'Are you okay? Are you hurt?'"

Kirkpatrick also suggested that "nobody's changed one bit" in the decade since *NSYNC were last together but played down rumors of a reunion tour, saying this performance was "for Justin".

"It was funny, because all of us getting back together, we remembered what we like about each other and we remembered what we hate about each other," he joked.

"It was just a lot of fun. And I think every one of us, even JC, the quiet one, was just enjoying the moment and revelling in what Justin had accomplished and really honored in the fact that he asked us to come back and perform with him.

"I'm not going to say it's never going to happen [again], but it was what it was."

Kirkpatrick joked that Joey Fatone was immediately suggesting a longer reunion backstage, but pointed out that a hypothetical tour would take "weeks and weeks" to prepare for.

"It takes a lot of work," he said. "Everything we did with the music, with everything, it wasn't just, 'Hey, let's do it, let's put it out', whatever. Let's do it, keep doing it until we're happy with it and it's right and we feel comfortable with it. And that's the way we look at touring."